The present invention relates to devices for measuring the rate of infiltration of liquids into soil. Such devices are generally known as percolation gauges or percolation testing devices.
Determining the rate at which liquids will infiltrate a soil is often important in ascertaining the potential of a specific soil for a particular use. Most frequently, infiltration rates are measured to determine the surface area requirements of underground sewage disposal systems. Additionally, rainwater run-off sites, adjacent proposed asphalt or other ground covering development projects, must be evaluated as well.
When water or other liquids infiltrate a soil, some of the liquid will be absorbed by the sponge-like soil particles. Any remaining liquid will percolate or leach through the soil, by the force of gravity, to underground drainage areas. The relative amount of liquid that can percolate through the soil depends primarily on the level of the soil's saturation. If the soil is thoroughly saturated, any additional liquid will be forced to percolate through it.
Unfortunately, in testing the rate of infiltration, it is impossible to completely saturate a test soil. Consequently, any measurements necessarily include both the rates of absorbed and percolated liquid as sub-components of the overall infiltration rate. Typically, the test soil is "pre-soaked" in an attempt to approximate a heavy saturation of the soil. In some regions, the tests are only given during the wettest times of the year to increase the probability that the soil will be as saturated as possible.
After a set pre-soak period, measurement of water infiltration takes place. In the art, these measurements have come to be known as "percolation" tests, although the term is not accurate. For example, a particularly porous or sandy soil may absorb all test liquid even though none of the water percolates through a fine-particle, or clay-like, soil layer beneath the sandy soil. Nonetheless, the soil would have performed well in the "percolation" test. Because it is common in the art, as shown in the references cited below, the term "percolation" will hereafter, for the purposes of this specification, be interpreted as being synonymous with the term "infiltration", as described above.
A percolation test is administered at a test site by excavating the subject soil at least to the level of the proposed liquid input, e.g., the level of output of a septic tank's effective leeching field. Then, a test hole or "bore hole" is dug, generally twelve inches wide and eighteen inches deep. Water is poured into the test hole until it reaches a certain depth. Typically, a specific pre-soak period is prescribed, during which the water level in the test hole is maintained at a constant height. After that period, no more water is added and either the height of the water in the test hole is recorded at set time intervals or the time is recorded for that height to descend to incremental levels.
Many problems exist in both the apparatus and method used to effect such measurements. Initially, simple measuring sticks or rulers were inserted into the test hole at the prescribed times and the height of the column of water visually observed and recorded. Or, the ruler was left in the hole and the times recorded when the water level had descended to the prescribed incremental heights.
Such methods invited numerous problems. For example, inserting rulers at different intervals ignored possible alteration of the depth of the test hole due to changes in the soil at its bottom. Also, other problems arose if the person recording the measurements had to move in and out of the excavation site, next to the test hole, to take the readings at the various intervals. This increased the possibility of debris falling into the test hole, or even its collapse.
Additionally, the prior measurement apparatus forced observers to stand almost over the test holes to view the results, further encouraging disruption of a hole. Also, the results from "ruler-type" testers were difficult to view. As the water descended toward the bottom of the test holes, those testers were difficult to read because they included no clearly visible gradation markings.
Improvements over the early percolation test art are well known U.S. Pat. Nos. 3,945,247, 4,099,406 and 4,341,110 all disclose free standing cylinders with complicated mechanisms for remotely measuring the percolation test results. These types of percolation test devices avoid many of the problems of the older art associated with intrusion upon the test hole and viewing the measuring device. Nonetheless, use of complex mechanical timers, electrical probes, and electro-mechanical marking devices under all-weather environmental conditions have rendered such types of apparatus costly and unreliable.
Accordingly, it is the primary object of the present invention to provide a new method and apparatus for administering percolation tests that affords remote observation of the test results without the need for complicated electro-mechanical timing and marking components.
It is another object to provide a new percolation testing method which produces reliable and consistent results.
It is another object to provide a percolation testing method wherein the person administering the test can record the results without having to descend into the excavated site near the test hole.
It is yet another object to provide a percolation testing apparatus having gradation indicators that are easily adjustable so that the apparatus may be utilized both in tests that record the time variable and tests that record variations in water height.
It is a further object to provide a percolation testing apparatus that is durable, yet of simple construction and therefore inexpensive to manufacture.
The above and other objects and advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.